Natural oils, such as seed oils, and their derivatives can provide useful starting materials for making a variety of chemical compounds. Because such compounds contain a certain degree of inherent functionality that is otherwise absent from petroleum-sourced materials, it can often be more desirable, if not cheaper, to use natural oils or their derivatives as a starting point for making certain compounds. Additionally, natural oils and their derivatives are generally sourced from renewable feedstocks. Thus, by using such starting materials, one can enjoy the concomitant advantage of developing useful chemical products without consuming limited supplies of petroleum. Further, refining natural oils can be less intensive in terms of the severity of the conditions required to carry out the refining process.
Natural oils can be refined in a variety of ways. For example, processes that rely on microorganisms can be used, such as fermentation. Chemical processes can also be used. For example, when the natural oils contain at least one carbon-carbon double bond, olefin metathesis can provide a useful means of refining a natural oil and making useful chemicals from the compounds in the feedstock.
Metathesis is a catalytic reaction that involves the interchange of alkylidene units among compounds containing one or more double bonds (e.g., olefinic compounds) via the cleavage and formation of carbon-carbon double bonds. Metathesis may occur between two like molecules (often referred to as “self-metathesis”) or it may occur between two different molecules (often referred to as “cross-metathesis”). Self-metathesis may be represented schematically as shown below in Equation (A):Ra—CH═CH—Rb+Ra—CH═CH—Rb⇄Ra—CH═CH—Ra+Rb—CH═CH—Rb,  (A)wherein Ra and Rb are organic groups.
Cross-metathesis may be represented schematically as shown below in Equation (B):Ra—CH═CH—Rb+Rc—CH═CH—Rd⇄Ra—CH═CH—Rc+Ra—CH═CH—Rd+Rb—CH═CH—Rc+Rb—CH═CH—Rd,  (B)wherein Ra, Rb, Rc, and Rd are organic groups. Self-metathesis will also generally occur concurrently with cross-metathesis.
In recent years, there has been an increased demand for environmentally friendly techniques for manufacturing materials typically derived from petroleum sources, which can be made by processes that involve olefin metathesis. This has led to studies of the feasibility of manufacturing biofuels, waxes, plastics, and the like, using natural oil feedstocks, such as vegetable and/or seed-based oils.
Natural oil feedstocks of interest include, but are not limited to, oils such as natural oils (e.g., vegetable oils, fish oils, algae oils, and animal fats), and derivatives of natural oils, such as free fatty acids and fatty acid alkyl (e.g., methyl) esters. These natural oil feedstocks may be converted into industrially useful chemicals (e.g., waxes, plastics, cosmetics, biofuels, etc.) by any number of different metathesis reactions. Significant reaction classes include, as non-limiting examples, self-metathesis, cross-metathesis with olefins, and ring-opening metathesis reactions. Non-limiting examples of useful metathesis catalysts are described in further detail below.
Refining processes for natural oils (e.g., employing metathesis) can lead to compounds having chain lengths closer to those generally desired for chemical intermediates of specialty chemicals (e.g., about 9 to 15 carbon atoms). By using these compounds as starting materials, it is possible to create a variety of novel chemical compounds that may be used for a variety of useful purposes. Further, because these compounds contain somewhat different chemical functionality than similar molecular-weight compounds derived in other ways, metathesis-derived variants may have beneficial properties that could not have been appreciated otherwise.
Meanwhile, the use of certain industrial solvents has curtailed in recent years due, in part, to concerns over their impact on the environment and their effects on general health and safety. This is especially true of solvents known to have a high volatile organic content (VOC), as such compounds may contribute to greenhouse gas production and ozone depletion. In some instances, traditional high VOC solvents can also be carcinogenic, teratogenic, toxic, and/or mutagenic. Therefore, a number of common solvents have come under increased regulatory scrutiny and therefore suffer from decreased use. Such solvents include aromatics (e.g., benzene, toluene, xylenes, and the like), ketones (e.g., methyl ethyl ketone, methyl isobutyl ketone, and the like), halogenated organics (e.g., dichloromethane, perchloroethylene, and the like), glycol ethers, and alcohols (e.g., methanol, isopropanol, ethylene glycol, and the like).
Certain derivatives of renewable feedstocks can provide more suitable alternatives to high VOC solvents. For example, fatty acid alkyl esters (e.g., from the transesterification of vegetable oils, animal fats, or other lipids) can provide environmentally friendly alternatives to traditional oxygenated solvents. Methyl soyate, for example, has a low VOC value, a high flash point, a low toxicity, and a high biodegradability. Terpene oils from citrus and pine (d-limonene and pinene, respectively) may also serve as suitable alternatives to certain traditional organic solvents.
Such renewable solvents are not without their problems, however. For example, d-limonene and dipentene (a racemate of d-limonene) are both acute and chronic aquatic toxins, and also have an irritating and sensitizing effect on the skin. Further, d-limonene is highly inflammable (e.g., more so than petroleum distillates) and can be subject to fluctuations in supply and price. Fatty acid alkyl esters can overcome some of these deficiencies of terpene oils, but can also exhibit poor solvency relative to certain incumbents.
Thus, there is a continuing need to develop solvent compounds and compositions that are renewably sourced, exhibit high solvency, and have a desirable health and safety profile (e.g., in terms of toxicity and VOCs).